The present invention relates to apparatus for operating the intake or exhaust valves of an internal combustion engine. More particularly, the invention relates to such apparatus in which a plurality of adjacently positioned, pivotally mounted cam followers open and close the valves in response to the rotation of cams on a camshaft driven in synchronism with the operation of the engine and in which the respective cam followers are connected or disconnected for operation in unison or independently by selectively actuated, hydraulically operated couplings for imparting various modes of operation to the valves.
One such valve operating apparatus of the concerned type is shown and described in U.S. patent application Ser. No. 009,239, filed Jan. 30, 1987 and assigned to the assignee herein. In such apparatus the cam followers are pivotally mounted on a rocker shaft having a hollow interior defining the hydraulic pressure supply passage to the respective couplings. The hydraulic pressure is supplied independently to the hydraulic pressure chambers of the respective couplings to operate pistons therein in cooperation with return springs. In such prior art valve operating devices the return springs in the respective couplings have the same set load and, in order to provide independent hydraulic pressure supply passages to the respective hydraulic pressure chambers, it is necessary to force and fix a steel ball in the rocker arm shaft in order to divide its interior into independent passages communicating with the hydraulic pressure chambers of the respective couplings. This results in the need for a complex hydraulic pressure supply circuit.
It is to the amelioration of this problem that the present invention is directed.